That the superior colliculus is intimately involved in visually-guided behaviors has been known for some time. Because the maturation of the superior colliculus is a protracted postnatal event, it offers a unique opportunity for correlating anatomical and physiological data directly with the chronology of visuomotor behaviors. Since the receptive field properties of its cells serve as selective 'gates' to the circuitry of the superior colliculus and thereby determine which stimuli elicit visually-guided behavior, a host of studies of these properties have been conducted in developing animals. Because visual cells are concentrated most heavily in the superficial laminae of the structure, this is the population that has been examined most closely. More recent information indicates, however, that these are not the cells most directly involved in visually-guided behaviors. Rather, it is the deeper laminae cells, whose axons project to motor and premotor areas, that are most relevant. These cells receive different visual afferents than do superficial laminae cells and may show substantially different ontogenetic time courses and have different developmental requirements that reflect their differing behavioral roles. Unfortunately, we know very little about the maturation of deep laminae cells or the development of the corticotectal afferents that determine their complex receptive field properties. In the next 5 years we will employ a multidisciplinary approach that will not only document the maturation of deep laminae receptive field properties but will also determine the maturation of corticotectal afferents (from lateral suprasylvian cortex) and the behaviors dependent on these afferents. We will employ anatomical, behavioral, histochemical, and physiological techniques in an effort to produce a comprehensive evaluation of the maturation of deep laminae visual cells, and thereby begin realizing some of the objectives that originally prompted much of the interest in the development of the superior colliculus.